This disclosure relates to nanocomposites comprising telechelic ionomeric polyesters and organoclays, their methods of manufacture and articles formed therefrom.
Nanocomposites are class of composites that are particle-filled polymers for which at least one of the dimensions of the dispersed phase is in the nanometer range (typically 10-250 nm). Polymer layered nanocomposites often have superior physical and mechanical properties over their microcomposite counterparts, including improved modulus, reduced gas permeability, flame retardancy and improved scratch resistance. Moreover, the nanoscale dispersion of the filler does not give rise to the brittleness and opacity typical of composites.
Polymeric, intercalation-type nanocomposites have been the subject of extensive research over the past decade. Much of the work in this area has been focused on polymeric nanocomposites derived from layered silicates such as montmorillonite clay. When the silicate platelets are isotropically dispersed in a continuous polymer matrix, the material is termed “exfoliated.” The best enhancements in physical properties can be achieved with an exfoliated morphology. Polymer nanocomposites comprising a semicrystalline polymer matrix are particularly attractive, due to the dramatic improvement in heat distortion temperature and modulus provided by the nanoparticle reinforcement and the high flow character inherent to most commodity semicrystalline thermoplastics such as nylon-6, nylon-6,6, poly(butylene terephthalate), poly(ethylene terephthalate), polypropylene, polyethylene, and the like. Because of these desirable characteristics, semicrystalline polymer nanocomposites have been shown to be well suited for application as injection moldable thermoplastics.
Sulfonated poly(butylene terephthalate) (PBT) random ionomers have been blended by reactive extrusion with organically modified montmorillonite. Because of the ionic nature of the sulfonate groups and their expected insolubility in the polyester matrix, the presence of the sulfonate groups provide a thermodynamic driving force for the production of nanocomposites derived from montmorillonite clays. Combining PBT-ionomers with montmorillonite clays results in exfoliation of the clays due to favorable electrostatic interactions between the charged surfaces of the silicate clay particles and the —SO3Na groups of the PBT-ionomer. As disclosed in U.S. application Ser. No. 11/001,214 (U.S. Publication No. 2006/0116464), the presence of ionic groups at the end of the polymer chain has a positive effect on the exfoliation of the clay and on the thermomechanical properties compared to compositions using unmodified PBT. In particular, Dynamic Mechanical Thermal Analysis (DMTA) analyses have shown a consistent increase in heat distortion temperature respect to commercial PBT (up to 55° C.) and to nanocomposites of standard PBT (30° C.). The observed improvement in DMTA has been attributed to the formation of ionic interaction between the polymer end groups and the charged surface of the clay. Telechelic ionomers present a consistently lower melt viscosity compared to random ionomers, since the interaction between the ionic groups give rise only to an electrostatic chain extension and not to the formation of a crosslinking, as is the case in random ionomers. Therefore, in contrast to random ionomers, where only low weight average molecular weights (Mw) can be obtained, high molecular weight telechelic ionomers can be successfully obtained.
Nonetheless, there remains a need in the art for nanocomposite polymer compositions that feature additional enhancements for use in the development of such materials. In particular, it has been difficult to obtain an optimal balance between the ductility and the flexural modulus of nanocomposites.